Power line communication systems are becoming more and more widespread. Many different systems and standards are developed. As more and more systems will be deployed, co-existence becomes increasingly important. Undoubtedly, Frequency Division Multiplexing (FDM) is the most straightforward way to achieve co-existence between different systems. Different communication channels are allocated to different frequency bands, the bandwidth of which depends on the service requirements. In order to achieve high data rates, through a higher number of channels, the system bandwidth is specified up to 60 MHz (or higher) so that emerging multimedia services such as IPTV, HDTV, etc. can be supported.
FDM poses significant design challenges in the Analog Front-End (AFE), specifically on the receiver (RX) part of the AFE. Especially because it captures the complete used spectrum and the properties of the received signal spectrum depend on many (poorly known) factors. For this reason, conventional AFE architectures, designed for TDMA schemes, are not really suited to support FDM, while FDM will be required to support co-existence.
Conventional PLC transceivers employ a straightforward architecture in the RX path mainly consisting of a low-noise amplifier (LNA), a low-pass filter (LPF), a variable gain amplifier (VGA) and a high speed analog-to-digital converter (ADC) digitizing the complete frequency band, as shown in FIG. 8. This is a very good architecture for TDMA based communication, in which the available bandwidth is assigned to a single user in a certain timeslot. However in an FDM system, the spectrum is shared by a number of users, resulting in simultaneous communication channels, each having different properties. As a consequence, taking into account the powerline uncertainties and an FDM scheme, the requirements on AD converters are huge if a minimum SNR is required in bad conditions, especially for the next generation PLC systems up to 100 MHz (as considered in the IEEE P1901 working group).
In the prior art, solutions have been developed for particular FDM PLC systems without digitizing the full frequency band. These FDM front end solutions can be split into two groups. The first group carries out a frequency conversion to a high intermediate frequency (IF) followed by band-pass filters and subsampling. An example of the first group can be found in WO 2004/091113. A system and a method for data communication over a power line are presented. The up-conversion is carried out in the receiver path where the received signal is filtered by off-chip, fixed, expensive band-pass filters. Subsampling of the signal is done at a high intermediate frequency, which is sensitive to clock jitter. The system requires band-pass filters at high IF (order of 100 MHz). At higher frequencies, the required Quality factor is higher in order to achieve the same amount of channel filtering, which makes the band-pass filters less effective at higher frequencies due to technological limitations. Furthermore, band-pass filters at high IF (order 100 MHz) cannot be integrated on chip with good noise and linearity performance, which is important from a cost point of view.
The other group uses simple fixed band-pass filters followed by subsampling Analog-to-Digital conversion, without applying a frequency conversion (e.g., U.S. Patent Publication No. 2002/186715). The fixed band-pass filters provide very little flexibility for the channel allocations. This is a disadvantage because the channel characteristics are unknown and changing with time. Moreover, co-existence with other systems requires flexibility to allocate the channels because other systems could use different channels widths, or different center frequencies. Band-pass filters cannot be integrated as good as low-pass filters (filter order, noise, distortion, complexity, power consumption etc.).
Prior art power line AFEs, which require supporting FDM, are not optimized for best performance (higher SINAD, dynamic range, robustness against interferers) and ASIC integration.